Method of drilling wells



Sept 5, 1944 w. v. vll-:TTI ET AL. 2,357,565

METHOD OF DRILLING' WELLS Original Filed Oct. 5, 1955 L: 'f" 'ff 'uw Patented Sept. 5, 1944 UNiTs METHOD F DRILLING WELLS William V. Vietti and Allen D. Garrison. Houston, Tex.. assignors to The Texas Company, New York, N. Y., a corporation of Delaware Original application October `5, 1935, Serial No. 43,774. Divided and this application December I 9. 1943, Serial No. 513.560

2. claims. (ci. faz-8.5)

This invention relates to drilling muds and more particularly to the conditioning of drilling muds employed in the drilling of wells.

This application is a division of our application Serial No. 43,774, led October 5, 1935.

More specifically, our invention relates to the control of the viscosity and colloidal propertiesof drilling muds by the addition thereto of chemical and colloidal compounds, whereby the drilling muds are at all times maintained ir. a state which permits them to fulll their functions most successfully. v

Drilling muds are almost universally used in the drilling of wells employed for tapping underground collections of oil, gases,brines, and water. These muds fulfill various functions, the most important of which are to assist in the removal of cuttings 'from the wells, to seal off formations of gas, oil, and Water which may be encountered at various levels, and to lubricate the drilling tools and the drill pipes which carry the tools.

Drillingmuds are essentially mixtures of clay and Water, usually so compounded that they weigh from about eight and one-half to fourteen pounds per gallon. Whenever it is found necessary to increase the specific gravity of a particular mud, it is customary to add thereto finelydivided materials which have a high specific gravity such as barytes, etc.

An ideal colloidal drillingmud is one which is thixotropic, that is to say, a iluidyvhich, on agitation by pumping or otherwise, has a relatively low viscosity and is free-flowing but, whenagitation is stopped, gradually sets or gels. This gelling action should be sumciently slow to permit the cuttings to settle two or three feet before the gel structure is strong enough to support them. When such a drilling mud is circulated through a Well, it picks up the cuttings and carries them to the surface and there, upon settling in a. settling pit, the cuttings settle out, leaving a substantially cuttings-free drilling mud.

The use of a drilling mud, which is highly thixotropic, is attended by many disadvantages, the more important of which will be discussed briefly. A highly tmxotropi mud is one which gels so rapidly that its viscosity reaches high values quickly, usually in from one to three seconds after agitation has stopped. Such a drilling mud is difficult to pump and, although it does effect the complete removal of cuttings from the well, it does not allow the proper separation of cuttings from the mud in the settling ditches and pits where the mud is in a semi-quiescent state. Furthermore, it will be observed that it clings to the drill pipe and the drilling tools and thus exerts an appreciable braking action. In addition to these undesirable properties, it has been observed that the us'e of a highly thixotroplc drilling `mud may cause gas blowouts ywherethe well traverses strata containing gases under high pressure. When drilling through such strata, the hydrostatic head of the drilling mud serves normally to more than counter-balance the gas pressure. During the drilling operations, when it becomes necessary to withdraw the drill pipe and the drilling tools,l the highly thixotropic drilling mud will cling thereto. In this manner the balance that has existed between the hydrostatic head of the drilling mud and the gas pressure is disturbed and, if the gas pressure is higher than the lessened hydrostatic head of the drilling mud, a gas blowout occurs.

The use of a. drilling mud, which is not thixotropic, is attended by some disadvantages, the more important of which will be discussed briefly: A non-thixotropic drilling mud is one which does not set or gel when agitation is stopped. `The viscosity of the non-thixotropic mud is low, and. therefore, removes cuttings from the well, in which it is employed, less eillciently than a mud which has a high viscosity. Furthermore, a nonthixotropic mud will not suspend cuttings in the hole, and a temporary cessation of drilling may allow sufcient 'time for the cuttings to settle back through the mud, and thus pack around the bit and drill pipe, making it impossible to pull the drill pipe when operations are resumed. The use of a non-thixotropic drilling mud also increases the possibility of losing the drilling mud in the well by loss of uid into porous formations.

The use of a non-thixotropic drillingmud has some advantages which may be utilized in drilling wells through indurated or partially indurated formations, as occur in certain areas. 'I'he more important of these advantages will be discussed briey. A non-thixotropic drilling mud is easy to pump and can effect the pumping and complete removal of cuttings in a well in which it is employed, provided the fluid velocities are maintained at sufllciently high values. kA non-thixotropic mud will not cling to the drilling pipe, and will not cause an unbalancing of the hydrostatic head exerted by the drilling mud in the well. A non-thixotropic drilling mud will allow the cuttings to drop out into the ditch and in the pits to a much higher extent than occurs in the highly thixotropic muds Gas entrained in the mud,

while passing through the gas-bearing strata, is quickly released. thus allowing the mud to regain its weight in the ditch and pit 'before being pumped back into the well.

Drilling muds may then be classiiled as nonthixotropic, thixotropic, or highly thixotropic, all of which consistessentially of 'colloidal dispersions, or semi-colloidal suspensions of clay lin water. The desirable mud to use is a mud which is thixotropic and none of the undesirable characteristics of the very slightly or very highly thixotropic drilling muds.

Drilling muds consist essentially of colloidal dispersions of clay and water. When this is considered. in commotion with the further fact that the thixotropic character of a drilling mud is a function of its colloidal condition. it lbecomes obvious that the clay particles.. having a sise within the colloidal particle size range, determine other factnrsu'nknown to us.

This type of conversion could produce drilling muds which could be used were the conversion complete. A complete conversion would result in an acid clay mud, or in a polyvalent clay mud. These muds would be sensitive' to ilocculation, and although usable would not be desirable, because oftheirinherent sensitiveness in use, partlclllai'ly if it might be desirable t0 add treatin! largely the thixotropic character of a drilling mud. 'Ihe aforementioned colloidal .particles of clay are essentially acids whose anion is a micell where X is approximately l, Y is approximately 3, and Z may vary over wide values.

In the interests of simplicity, the aforementioned anion will be termed hereinafter as clay and the compounds formed by its combination with various cations will be termed clays of such cations; so, for example, the hydrogen compound will ybe termed hydrogen clay or; acid clay, the sodium compoimd will be termed sodium clay, while'the calcium compound will be called calcium clay. For purposes of thisy discussion, we consider several typesv ofclays, acid or hydrogen clays; polyvalent ion clays such as calcium or magnesium clays; monovalent'ion clays as exemplified by potassium clays and, iinally. a separate grouping of monovalent ion clays limited to lithium and sodium clays. We have discovered that the last mentioned class diil'ers in its properties from the broader class of inonovalent ion clays and, because of this, we have 'classified it separately. A We will now examine, briefly, the characteristics of drillingmuds in which these various types of clays predominate. An acid clay, upon dispersion in water, yields a highly thixotropic drilling mud which insensitive to nocculation and which gels with great rapidity. Because of these properties, it is not desirable normally for use as a .drilling mud. Similarly, drilling muds formed by the dispersion in water of polyvalent ion clays or of monovalent ion clays other than lithium and sodium are sensitive to iiocculation and possess vcharacteristics of high gel rate and high vgel strength which render them undesirable forcommon use as drilling muds. We have discovered, however,l that drilling muds formed by the dis- -persion of lithium or sodium clays in .water are dispersions of the proper degreeof thixotropy which are particularly valuable when they are maintained within a pH range offrom 8.5 to 11.0. We, therefore. propose the use of drilling muds consisting essentially of dispersionsof sodium clays or lithium clays or mixtures of these in water, saiddispersions being maintained at a hydrogenl ion concentration of from 8.5 to 11.0.

When a sodium or lithium clay drilling mud is employed, it has been found that through base exchange with hydrogen or polyvalent ion clay' strata,the sodium or lithiumciays may be-.con-

verted into either hydrogen or polyvalent ion clays. Such a reaction is highly undesirable since the final drilling mud is highly thixotropic and is not useful for the usualdrilling purposes. The

chemicals, 'or if these muds were used in drilling porous strata .containing alkaline waters.

Various means have been suggested for maintaining a drilling mud in a thixotropic state. If high, hydrogen ion concentrations are to be combatted,v alkali materials such as sodium hydroxide are incorporated in the drilling mud. This is an undesirable method of solving the problem because, if suiiicient alkali is employed. the pH of the drilling mud will be considerably higher than the upper pH range of a thixotropic drilling mud. f f

By our invention, we are enabled toavoid the disadvantages inherent in the aforementioned processes in that we render a thixotropic drilling mud highly resistant to both acidincation and to base exchange. We accomplish this result by providing as the aqueous phase of the drilling mud a buffer` salt solution containing disodium phosphate. .By using such a solution as the aqueous, phase of the drilling mud. the pH'of the drilling mud may be maintained within the range of from 8.5 to 11.0. We do not, however, intend i to limit ourselves to buffer salt solutions conr'weak acids.

taining only disodium phosphate, but contemplate the use of various mixtures comprising disodium phosphate and including such compounds as sodium or lithium hydroxides and water-solu- `bie salts such-as-sodium and lithium salts of boric, phosphoric, carbonio, oxalic, silicio, and similar Not only does the disodium phosphate maintain the hydrogen ion concentration relatively constant withinthe stable range for the particular -clay dispersions rin use, but'it also retards the rate of base exchange. However, since this salt'is an electrolyte-it has a tendency to cause the drilling mud to become coagulated. In order to avoid this, we have found it desirable to incorporate in the drilling mud small quantities of lyophile colloids such as quebracho, straw emulsion, dextrine.. starch, gallo-tannic acid, catechu. casein, and equivalent materials. f

We vhave discovered a particular mode of employing drilling muds treated in accordance with the aforesaid method which permits of the moet eifective drilling of wells. Wells are usually drilled by means offa rotating drill pointer tool, the rotary movement being imparted to it from thesurface through a hollow pipe or conduit. This pipe or conduit is situated within l casing or pipe, the diameter of which is slightly larger' than that ofthedrillingtooi. In'thecourseofthedrilling operation, a drilling i'iuid or mud is delivered into ing mud treatment.

being penetrated. I [t serves two primary purposes, the one to lubricate the drilling tool andthe other to remove the cuttings or debris which have been cut out of the strata by the drilling tool. The latter -is effected by the drilling uid rising upwardly through the casing iin the space between the inner wall of. the casing and the drill pipe and being discharged at the surface level.

When an ordinary drilling mud, consisting essentially of water and clay, is employed in the aforesaid manner, it will be'observed in many cases that although the mud, when first introduced into the drilling pipe, was a colloidal uid of the proper degree of thixotropy, upon emergence from the casing, it will have lost its desirable characteristics, usually being more or less gelled and, therefore, unsuitable for furtheruse. v

' mentioned lyophile colloids in the buffered drilling mud, it is possible' to minimize or neutralize the temporary occulation which the disodium phosphate may have upon the mud dispersion.'

The lyophile colloid may either be mixed with the buffer salt solution containing disodium phosphate or may be added to the drilling mud hefore or after the addition toit of the solution.

We have found that in many cases, it'may bek unnecessary to further treat the cuttings-laden drilling mud before delivering it to the settling pit where the cuttings are allowed to settle out. However, in some cases, it may be desirable to mix a further quantity of the buffer salt solution containing disodium phosphate which may'or may not contain a lyophile colloid with the drilling mud prior to its discharge into the settling pits.` By following this method of application, it is possible to maintain a drilling mud constantly in a condition in which it fulfills its function most successfully.

Our invention may be described further in connection with the drawing which sets forth in diagrammatic form a preferred scheme of drill- 'Ihe numeral l0 designates a storage tank for fresh mud consisting essentially of clay and wa; ter. vThis storage tank is connected through the line Il. valve l2, pump I3, valve I4, with the circulating tank l5, which serves. as a reservoir for the drilling mud circulation system. This tank. which may be provided with a suitable agitating device, is connected by means of the line I1, controlled by the valve 18, with a tank I9, containing a concentrated solution of' a. buier salt solution containing disodium phosphate and a suitable lyophile colloid. The tank I is connected by the line 20. controlled by the valve. 2l, with the pump 22, which discharges through the line 23, controlled by valve 24, into the drill pipe 25. This drill pipe, which is of conventional construction, extends into the earth and is fitted at'its lowermost point with a drilling or cutting tool 26. The casing 21 is concentrically tted around the pipe 25 and extends from the surface a varying distance into the hole which is being drilled. The space between the drill pipe and the casing communicates through the line 29, with the settling pit 33. through the valve 30, the pump 3|, and the valve 32. A line 34, controlled by valve 35, connects the storage tank I9 with the line 29 at a point intermediate the outlet of the casing 21 and the pump 3|. 'Ihe settling pit 33 is connected through the line 36, pump 31, and the valve 38, with the circulating tank l5.

In a typical application of our invention, in connection with the described apparatus, a suspension of clay and water isprepared in the storage tank I0 by suspending a given weight of clay in the properquantity of water. A denite quantity of this suspension is delivered into the circulating tank I5 and vthere is added to it a sumcient quantity of the concentrated solution of the disodium phosphate and lyophile colloid to bring the pH of the'mud within the range of from 8.5 to v11.0. After suitable. agitation, the alkaline drilling .mud is their deliveredby a suitable pump 22, into the drill pipe 25, passing downwardly through it andthrough the drilling tool, which is mounted at itszlower end. The mud picks up the cuttings'and loosened debris and -carries them upwardly in the space between the casing andthe drill pipe. At the surface, this mixture is discharged directly into the line 29, which delivers it to the settling pit 33. In those cases where the mud is found to have increased in viscosity, due to chemical changes undergone during its brief contact with the strata being drilled, it is desirable to inject into it a further quantity of the concentrated solution of the disodium phosphate and the lyophile colloid.

Upon remaining relatively quiescent in the settling pit, the cuttings and debris settle out, while the drilling mud remains in a state of stable suspension. There is continuously withdrawn from the settling pit at a strategic point, a sumcient quantity of cuttings-free mud to maintain a sufcient amount of mud in circulation. Y l We offer herewith several examples of the application of our invention to the treatment and conditioning of drilling muds. In the course of drilling a well in the Manvel neld, Brazoria County, Texas, the drilling mud, consisting essentially of a dispersion of clay in water having 'l a mixture of 100 pounds of disodium phosphate `and 44 pounds of quebracho dissolved in 100 gallons of water. After the treatment, kthe drilling mud was found to be of the proper degree of thixotropy, having a pH value of 9.1, a weight.

of 10.2 pounds per gallon and a viscosity of 58 seconds through the Marsh viscosimeter.

While'drilling another well in the same ileld in whicha like amount of drilling mud was used,

` the mud became occulated and, like the drilling mud used in the previously mentioned well, its viscosity was too high for measurement in the Marsh viscosimeter.` There was then added to vthe flocculated `drilling mud a solution of 50 pounds of disodium phosphate and 22 pounds of quebracho in 50 gallons of water. In a relatively short time, the viscosity was found to have dropped to seco ds.. The drilling mud was then treated with ln l-lalddimerml 5o pounds of disodium phosphate and 22 pounds of quebracho in 50 gallons of water and this further treatment Obviously many modiiicationsand variations of the invention as hereinbefore set forth. may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed. as are indicated in the appended claims.

We claim :V y

1. In the art of drilling and controlling wells. the method comprising circulating in the bore hole a mud containing an aqueous dispersion of clayey colloidal matter, and maintaining the mud ln a thixotropic state by adding to it in the course of its circulation a buier salt solution containing disodium phosphate,.and a lyophile colloid.

2. In the art of drilling and controlling wells, the method comprising circulating in the bore hoie a mud containingan aqueous dispersion of clayey colloidal matter, and maintaining the mud l* in a thixotropic state by adding to it ln the course ci its circulation a buier salt solution containing disodium phosphate. and Quebracho extract. j

Aim n. GARmso. 

